To my understanding, he bought shares, which incidentally paid no dividends, and wanted to offset an incidental cost incurred in the act of purchasing such shares (he used a computer in order to place his order in the market) against income from other sources.
Since his expense was linked to the purchase of an asset and not to the derivation of income, he was told that it could only in principle include such incidental cost in the cost base of the asset under the CGT legislation. In principle because it is doubtful that the ATO would ever accept more than a dollar or two as being reasonable.
Had he incurred the cost in the process of deriving income then he would be able to reduce his taxable income by the amount corresponding to such cost or even in an extreme case to carry the cost in question in the whole or in part forward as a tax loss.
In short, the problem is that he did not incur the cost while deriving taxable income.
